form_dropdown allowing to select only one item

[eluser]dinisptc[/eluser]

its using multiple in the html , how can i remove this

<select name="companyUID" id="contractorCompany" multiple="multiple">
<option value="">please select</option>
<option value="company_51b1a4fb87ea3">bcvbc</option>
<option value="company_51d55f5ac2344">sfsdf</option>
<option value="company_51d58175f248a">sfsdf</option>
<option value="company_51d5b4705989a">dddddddddddddd</option>
<option value="company_51d5bb11ddf12">firma do ze chagas</option>
<option value="company_51d5bb17df524">firma do ze chagas</option>
<option value="company_51d5bb27e2966">firma do ze chagas</option>
<option value="company_51d5bbb46e672">firma do ze</option>
<option value="company_51d5bbbf4dbed">firma do ze</option>
<option value="company_51d5bbcf17c30">firma do ze</option>
<option value="company_51d5bbd5721c6">firma do ze</option>
<option value="company_51d5bbdc13aab">firma do ze</option>
<option value="company_51d5bcdeebf32">firma do ze chagas</option>
</select>